The present invention relates to a resin molding method for protecting the winding of a resolver. The resin is to protect the winding, which is coiled around multiple magnetic poles of a stack of the resolver.
For example, consider a resolver that is used to detect a deviation angle. The resolver includes a rotatable, assembled rotor stack and a stator stack. The stator stack includes a coiled excitation winding and an output winding wound around multiple magnetic poles. The winding portion of the stator stack is typically coated with resin material such as a varnish to fix the windings and to improve the insulation properties.
However, in prior art coating methods, in which a resin material such as a varnish is applied to the winding portion, processes such as the drying of the resin material are complicated and the number of tasks include, for example, the management of the coating volume of the resin material and the management of the drying temperature. Thus, it is difficult to guarantee reliability of the protection structure of the winding portion.
Therefore, a method to protect the winding portion and a signal output portion by molding a resin layer on the winding portion and signal output portion of the resolver (resin molding method) has been proposed (see Japanese Unexamined Patent Application Publication 2001-324353 and Japanese Unexamined Patent Application Publication 2002-171737).
In a prior art molding method, at least the winding of the stack is molded by injecting a fused resin molding material into a space formed between a top mold and a bottom mold member, while the annular stack of the resolver, including a coiled winding, is sandwiched between the top mold and bottom mold member. However, in the case of thin (for example, a diameter of 0.08 mm to 0.14 mm) windings, defects such as a disconnection or a layer short circuit may occur due to the effect of environmental conditions on the resin molding material. Therefore, use of a thicker winding and use of a partial molding have been employed. However, the molding method of the prior art has additional problems as follows.
The stator stack of the resolver is structured such that thin silicon steel plates, which are press punched into an annular shape, are laminated and then adhered or crimped. There is non-uniformity in the thickness of the silicon steel plate, and this non-uniformity is accumulated across a number of the silicon steel plates. Therefore the thickness of the stator stack is not uniform. There is variation of 8 to 10% in the thickness of a single silicon steel plate. A variation equal to the number of silicon steel plates multiplied by 8 to 10% is produced in the thickness of the stator stack. Therefore, gaps are generated between the stator stack and the mold during the resin molding, and stabilization of the dimensions is difficult.